Rheology of Polyurethane Resin during Polymerization

Abstract

This report is made of the measurement of the changes of viscoelastic and dielectric properties and infrared spectrum during curing of polyurethane resin, and of their comparison with the internal stress produced during the formation of the thin resin layer on wood. The results are summarized as follows:(1) In the results on the apparent dielectric loss, is traced the process of freezing in the rotational motion of the segments along the main chain of polymer which contributes to α relaxation.(2) The two peaks are observed in the curve of logarithmic decrement, and they are attributed to the structural changes due to the transition, liquid-to-rubber and rubber-to-glass respectively.(3) The following equation on the modulus of dynamic rigidity has been induced from the results of infrared absorption measurement, and it agrees well with the experimental values.G(t)=ΔG(1-e-t/τ)+G0τ in this equation is the average relaxation time of the rotational motion of segments along the main chain of polymer, and equals to the reciprocal of rate constant on the reaction between NCO and OH groups. The apparent activation energy calculated from the slope of ln τ-T-1 curve is 6.65kcal/mol.(4) The changes of the internal stress produced during curing of resin layer on wood are also expressed by the segmental motion along the main chain of polymer.